The invention relates to a braking body, which is constructed as a brake block or a disk brake pad, comprising a supporting body with recesses as well as friction material elements arranged in the recesses.
Two large classes of friction brakes exist particularly in the case of rail vehicles. These are, on the one hand, the so-called block brakes and, on the other hand, the disk brakes.
The block brake is a friction brake for rail vehicles which can be constructed at reasonable cost. In the case of such a braking device, only an application device is required to press the brake block onto the running surface of the rail wheel. With respect to the construction of block brakes, reference is made to xe2x80x9cBrakes for Rail Vehicles, Manualxe2x80x94Brake-Related Terms and Valuesxe2x80x9d, Knorr Bremse AG Mxc3xcnchen, 1990, Pages 22 to 23 as well as Page 41.
A disadvantage of the block brake according to the prior art is particularly the high stressing of the wheel running surface which shortens the service life of the wheel, as well as roughening of the wheel running surface and rail corrugation. Particularly the latter effects result in a high running noise during the rolling operation of the wheel. These disadvantages of the block brake have promoted the development and the use of the disk brake in modern passenger train cars.
In the case of a disk brake, brake disks are mounted on both sides of the wheel body. The brake pads act upon the brake disk. The pertaining wheel is braked because of the friction force.
Concerning the construction of disk brakes according to the prior art, reference is made to xe2x80x9cBrakes for Rail Vehicles, Manualxe2x80x94Brake-Related Terms and Valuesxe2x80x9d, Knorr-Bremse AG Mxc3xcnchen, Page 50.
Brake blocks with recesses have become known from a plurality of publications. Thus German Patent Document DE-C-277907 shows a brake block with recesses into which a felt material is introduced. The felt material projects beyond the supporting body, so that no common friction surface is formed with the supporting body.
The brake block known from German Patent Document DE-U-29500977 comprises bores which receive stoppers made of friction material. However, these are fastened on the supporting body only by a screw. An elastic or tilting mounting of the individual friction material blocks has not become known from German Patent Document DE-U-29500977.
From French Patent Document FR-A-2689195 and British Patent Document GB-A1089955, individual braking bodies, which have a recess and a friction material element movably arranged therein, have become known. However these represent no brake blocks on brake pads with several recesses.
The brake pads known from German Patent Documents DE-A-4301006, DE-A-4436457 and DE-U-9307017 comprise elastically or tiltingly disposed friction material blocks. However, these are arranged directly on the supporting body and form, particularly with the supporting body, no cohesive friction material surface.
In the case of block brakes as well as in the case of disk brakes, a general problem is the contact pressure between braking bodies; that is, the brake block and the wheel, as well as the brake pad and the brake disk.
Because of heat conditions of either the braking body the wheel or the disk as well as their wear, the actual braking power of the above-mentioned friction brakes is always significantly lower than the theoretically possible braking power according to the material constants.
In the case of block brakes, an additional factor in optimizing braking power is that, for running-related reasons, the wheel running surface forms a surface which cannot be developed. The brake block therefore often rests only on points on the wheel running surface and forms a line-shaped contact. Because of this contact, the block brake is considerably overstressed.
Another problem of the above-described brake systems is the contact pattern which is insufficient, for example, because of thermal expansions and axial displacements. Generally, the harder the material the poorer the contact patern. The poor contact pattern results in rail corrugation or cracking in the wheel running surfaces and, as a result, in a high noise development during the braking.
It is therefore an object of the invention to provide a braking body, particularly for block brakes or disk brakes by which the above-mentioned disadvantages can be overcome.
According to the invention, this is achieved in that the friction material elements are movably disposed in the longitudinal direction of the recesses in a supporting body. The friction material elements are mounted in the recesses with the mounting elastic elements in the direction of the recesses with the mounting elastic elements in the direction of the recesses or tilting, elements. The friction material elements can form friction material blocks which can form a friction surface with the supporting body.
As a result of the movably disposed friction material elements, the surface pressure of the braking body according to the invention is improved decisively.
Another advantage of the brake block of the present invention is the fact that, when the wear of the wheel is uneven or in the case of an axial displacement, the individual friction material elements blocks can shift the recesses and therefore adapt themselves to the running surface of the wheel. Despite this displacement, the elastic or tilting suspension ensures essentially always the same surface pressure. In particular, always the same surface pressure is ensured independently of the axial position or wear.
In different embodiments of the invention, the recesses are arranged with the friction material elements either in series or offset with respect to one another.
A preferred embodiment of the invention is one in which the friction surface of the friction material elements constitutes a percentage of at least 30%, preferably 50 to 80%, of the entire friction surface of the braking body.
The elastic mounting of the friction material elements by elastically deformable bodies, such as spring elements, offers a number of additional advantages during different braking operations, described herein.
If a constant braking occurs with a high application force, the elastically disposed friction material elements, after a sufficiently long braking time, will compress so far that the sum of the elastic forces corresponds approximately to the application force of the brake block or of the brake pad.
After the occurrence of a contact pattern change, for example, by the axial displacement of the wheel or by a thermal bulging, a compression or rebounding of the elastically disposed friction material elements will take place corresponding to their characteristic spring curve, while each wheel bulge wears out the supporting body more than the adjacent friction material element. The valley on the wheel surface situated between two bulges relieves the contact area of the supporting body, while the friction material elements move out in a spring-loaded manner and ensure a certain friction energy feed therefore also in the valley area. This counteracts the formation of so-called hot spots in the case of block brakes but also in the case of disk brakes.
During constant braking with a lower surface pressure, after the release of the brake, a condition of the braking body will occur in which the friction material elements protrude with respect to the supporting bodies because the elastic elements, such as spring elements, relax.
If, starting from this condition, a slight braking takes place, the friction material elements are pressed into the recess only slightly and remain protruding with respect to the friction surface of the supporting body. Only a long or frequent braking by means of a low contact pressure force will have the result that the friction material elements will abrade and form a friction surface in a surface-flush manner with the supporting body.
During brief brake applications, two alternatives are conceivable.
In a first alternative, the friction material elements protrude at the start of the braking. Also in this case, a relatively uniform surface pressure occurs and thus a uniform introduction of energy into the wheel and the brake disk, which is defined by the elastically embedded friction material elements.
As an alternative thereto, before the start of the braking, the surface of the supporting body and of the friction material elements can close off almost flush. In such a case, the supporting body acts like a soft brake pad which, as a result of its elasticity, adapts itself to the wheel topography. The friction material elements elastically arranged in the recesses act in the same manner.
Spring elements are used as elastic elements. Specifically, the spring elements can be for instance, cup springs, flat coil springs, rubber rings or small rubber plates.
As an alternative to the elastic elements, the same effects can be achieved when the movable mounting of the friction material blocks comprises tilting elements which permit a movement of the friction material elements in the direction of the longitudinal axis of the recess because of tilting movements of the tilting elements.
In a further embodiment, several tilting elements can be arranged above one another, which mutually couple and thus form a superset tilting element.
In order to reduce the friction between the individual friction material elements and the recesses in the supporting body, it is advantageously provided that, between the interior wall of the recess and the friction material elements, devices are provided for reducing friction. Such sleeves may be made of sheet metal, which are fitted into the recess, and are particularly useful for this purpose.
The above-described preferred embodiments of the invention are achieved when the supporting body consists of a softer and more wear-prone material than the individual friction material elements.
In contrast, the friction material elements are preferably constructed of a temperature-stable, hard, wear-resistant material with a high modulus of elasticity in order to be able to achieve high brake performances. In particular, reference is made here to the use of quartz-bound high-temperature friction materials or sintered materials which are produced from superfine metal powder which comprises, for example, iron, copper and nonferrous metals.
In a further development of the invention, the friction material elements situated in a recess are combined to an individual friction material block which may have a circular-cylindrical shape. In this context, friction material blocks with, for example, nine individual elements can be arranged in a matrix and can be connected with one another, for example, by an adhesive substance or an equivalent.
The cylindrical friction material element can preferably be received in a recess in the supporting body constructed as a circular bore.
In addition to a circular-cylindrical shape of the friction material elements and of the recesses, other shapes can also be used, for example, with an n-cornered or elliptical cross-section of the individual friction material elements.
In the case of more expansive friction material elements or friction material blocks, a mat, for example, made of a caoutchouc-elastic material is advantageously used as the elastic layer instead of individual spring elements.
In one embodiment, the braking body according to the invention is provided as a brake block in conventional block brake units. For such an application, it is advantageous for the linking of the braking body according to the invention to the brake block shoe or the operating device to take place in a conventional manner according to the UIC Standard.
As another embodiment, the braking body can be used in a disk brake. Here also results similar to those with respect to the use of block brakes are achieved. In particular, when using hard, wear-resistant materials, a good contact pattern is achieved in many different operating situations, particularly because the pad surface adapts to the uneven friction surface of the brake disk so that the formation of hot spots is prevented. In addition, a high muffling of noises is achieved because of the elastic mounting.